1. Field of the Invention
The invention relates to active halogen containing bleach particles and a method for bleaching substrates through slow uniform release of halogenating agent.
2. The Prior Art
Chlorine bleaches are well known for their efficacy in cleaning and removing stains. For instance, in the fabrics washing area liquid hypochlorite solutions have gained a preeminent position in the market. These solutions, however, have one major deficiency. Liquid hypochlorite solutions are sufficiently potent that at high use levels they are known to damage colored fabrics. Typically, a consumer doses approximately one cup of 5.25% hypochlorite solution to a wash load. Concentrations of approximately 160 ppm available chlorine are thus present in the wash liquor.
It has been determined that chlorine contents of 30-40 ppm available chlorine do not attack colored fabrics to any great extent. Achievement of such limited concentrations require that release of active chlorine be controlled, particularly during the fill cycle of an automatic washing machine. Much research has focused upon coating or encapsulating chlorinating agents, e.g. dichloroisocyanurate granules, to obtain delayed slow release of active oxidant.
There are, however, also problems associated with encapsulated bleach particles. When used for cleaning clothes in automatic washing machines, the detergent will occasionally be trapped in the fold of a fabric. Dissolution and dissipation of the bleach to the bulk of the wash bath is interfered with. Local high concentrations of bleaching actives thereby come into contact with fabric surfaces. Under these conditions of entrapment, very small spots of severe localized dye damage resembling pinholes appear on the fabric.
U.S. Pat. No. 4,136,052 (Mazzola) reports to have solved the pinhole problem caused by localized high concentrations of bleach. The patent provides a special coating which encapsulates the bleaching compound. An active chlorinating agent is surrounded by a first non-reactive coating combination of fatty acid and wax. A second coating is applied containing fatty acid with a material exhibiting inverse aqueous solubility with respect to temperature. The outer, second coating is more resistant to dissolution in hot than in cold water. By this means, sufficiently delayed bleach release is provided in hot water to prevent pinholing.
U.S. Pat. No. 3,908,045 (Alterman et al.) discloses dichloroisocyanurate salts encapsulated with a first coating of a saturated fatty acid surrounded by a second coating of soap. The latter coating is formed by treatment of portions of the inner fatty acid shell with a solution of an alkali metal hydroxide.
Organic coating materials protect the bleaching agent in the foregoing patents. A slightly different approach is reported in U.S. Pat. No. 3,112,274 (Morgenthaler et al.). Inorganic salts such as sodium tripolyphosphate are applied in a fluidized bed to coat polychloroisocyanurate salts. The resultant encapsulated salts are said to be protected from decomposition by the attack of moisture, air or other reactive materials.
None of the prior art coatings surrounding the chlorine bleach provide adequate protection against pinhole type fabric damage for effective commercial exploitation, although protection is better at low and medium temperatures. Unfortunately, at hot wash temperatures above the melting point of the coating materials, pinholing is still a problem. To solve the problem, average coating weights have been increased by as much as 50% over the known art. Even these increased thicknesses do not ensure complete absence of pinholing at hot wash temperatures. Very thick coatings, which do control pinholing, are deficient because they nearly eliminate chlorine release at low wash temperatures.
Consequently, it is an object of the present invention to provide bleach particles which eliminate pinholing yet have satisfactory active halogen release at all wash temperatures.
Another object of this invention is to provide a method for bleaching various substrates including fabrics.